Negative electrodes for carbon arc lamps



March 12, 1968 A. PERRIN 3,373,308 NEGATIVE ELECTRODES FOR CARBON ARCLAMPS Filed July 5. 1966 2 SheetsSheet l 1 1 13a 1 f I Inventor JEAN A.PERRIN A [to s March 12, 1968 J. A. PERRIN 3,373,308

NEGATiVE ELECTRODES FOR CARBON ARC LAMPS Filed July 5. 1966 2Sheets-Sheet 2 Fig.5.

Inventor J. A- ERRM Attorneys United States Patent 3,373,308 NEGATIVEELECTRODES FOR CARBON ARC LAMPS Jean Adrien Perrin, Pagny-sur-Moselle,France, assignor to Societe le Carbone Lorraine, Paris, France, a Frenchbody corporate Continuation-impart of application Ser. No. 337,763, Jan.15, 1964. This application July 5, 1966, Ser. No. 575,203

Claims priority, application France, Oct. 31, 1963, 952,421, Patent1,383,904 Claims. (Cl. 313-357) ABSTRACT THE DISCLOSURE A negativeelectrode for a high-intensity carbon arc lamp has a male end oftruncated conical shape terminating in a conical point of greater apicalangle. This male end fits into the complementarily-shaped female end ofa preceding electrode. The electrode burns from the male towards thefemale end and at the junction the cathodic spot of the arc isconstrained to pass to the point so minimising risk of dowsing the arc.

This is a continuation-in-part of my copending application, Ser. No.337,763, filed January 15, 1964.

The present invention relates to carbon arc lamps and to an improvedmethod for the operation thereof Negative electrodes for such are lampsare usually made from a carbonaceous composition, e.g. an artificialgraphite or a coke bound with tar or a resin, or a mixture of artificialgraphite and coke bound with tar or a resin. Such a composition isextruded from a press in the form of cylindrical rods which are thenbaked at high temperature. The rods thus obtained are known asgraphitised.

Negative electrodes of such compositions are consumed at such a speedthat it is necessary to advance them gradually by roller wheels andafter a certain period of operation to extinguish the arc lamp and toreplace the negative electrode by a new electrode.

It is an object of the invention to avoid the necessity of extinguishingthe arc lamp to replace the negative electrode.

In conventional and relatively low intensity carbon arc lamps usingcurrents of about 8 to 17 amperes, stability of the position of thecathodic spot of the arc has not been an important requisite.Disturbance of the arc at the moment of its passage across an electrodejoint did not present any major problems, since the length of the arcwas very short, 3 to 5 mm. Also absolute maintenance of the cathodicspot along the axis of the negative electrode was not rigorouslynecessary. On the passage of the joint, there could be displacements ofthe cathodic spot without risk of causing an extinction of the arc. Thiswas because the low intensity used by the arc lamps for public lightingin 1884 did not induce a magnetic field sufiiciently intense to cause asa result during the passage of the joint, displacements of the are whichcould be aggravated by the magnetic field and result in the extinctionof the are. High intensity arc lamps, on the other hand, function atintensities of 200 to 400 amperes. The length of the are for these lampsis distinctly greater than that used for are lamps for public lighting:14-21 mm. for the high intensity arcs as against 3 to 5 mm. for the arclamps for public lighting. The magnetic field induced by the passage ofthe high current is so intense that when there is a slight displacementof the cathodic spot away from the axis of the negative electrode, thedisplacement is aggravated as a result of the action of the magneticfield on the plasma, which results in an extinction of the arc.

.It is known to make joints between positive carbons ice.

for are lamps operating on direct current, which allow arc projectorshaving a magazine of positive carbons to operate for long periods.However, although the negative carbons are used up much more slowly thanthe positive carbons, it is still necessary to replace them by newnegative carbon electrodes and for this it is necessary to switch offthe lamp.

It is an object of the invention to provide a negative electrode forcarbon arc lamps operating on direct current, said electrode being ofsuch nature as to allow an uninterrupted operation of the lamp, theelectrode being replaceable without cutting the input current andwithout the are being fortuitously extinguished when the cathodic spotpasses from the end of the negative carbon used up guring operation tothe beginning of the replacement car- It is a further object of theinvention to provide an improved negative electrode for carbon arc lampswhich is so fashioned as to enable a joint to be effected which avoidsextinctions of the arc, by maintaining the cathodic spot on the axis ofthe negative electrode at the moment of passage of the arc across thejoint.

It is another object of the invention to provide an improved method ofoperating a carbon arc lamp.

It is also an object of the inventionto provide a high intensity carbonarc lamp using negative electrodes which may be replaced simply withoutextinction of the arc.

Other objects will become apparent from the description which follows.

Accordingto the invention there is provided a negative electrode for ahigh intensity carbon are lamp, said electrode having a male end formedto fit into a complementarily-shaped female end of another electrode andbeing adapted to burn from said male end towards said female end, saidmale end being in the form of a truncated conical portion terminating ina pointed portion, the angle of taper of said pointed portion beinggreater than that of said truncated conical portion.

The essential advantage of the invention is that the replacement of thenegative electrodes may be effected quickly by hand, mechanically orautomatically without a binder, cement or similar jointing means, thejunction between two adjacent electrodes being effected by the fittingof a male end of the new electrode into a female end of thenearly-exhausted electrode.

The negative electrodes according to the invention are preferably usedwithout copper coating and in an arc lamp the current input of which islocated near the end of the cathodic point, that is to say at a distanceof 35 to 40 mm.

The relative dimensions and the taper angle of the mating parts are sodimensioned as to insure a good mechanical solidity of the joint withoutexaggeratedly diminishing the thickness of the skin electrode wall atthe location of the joint, as this could cause a breakage.

- In order that the invention may be more clearly understood, referencewill now be made to the accompanying drawings which show by way ofexample, two embodiments of known negative electrodes having truncatedjoints, and one embodiment of a negative electrode in accordance withthe invention, and in which:

FIGURE 1 shows an axial section through the end portions of two knownnegative electrodes having a truncated male spigot and a truncatedfemale socket,

FIGURE 2 shows a similar section of a second known arrangement,

FIGURE 3 shows a similar section through a negative carbon electrodeaccording to the invention, and

FIGURE 4 shows the co-operating ends of a pair of conjoinable electrodesaccording to the arrangement of FIGURE 3, but in the separated state,the left hand electrode being in axial section and the right handelectrode in elevation;

FIGURE shows in partial longitudinal vertical section a high intensitycarbon arc lamp in operation having joined negative electrodes accordingto the invention, and

FIGURE 6 shows in partial longitudinal vertical section the arc lamp ofFIGURE 5 when the burning negative electrode is almost consumed.

The negative electrode is provided with a male fitting at one end and afemale fitting at the other end, which fittings are arranged to coupleso that the normal passage of the electric current through the couplingis facilitated.

Referring to the drawings, and firstly to FIGURE 1, a known negativecarbon 1 shown in solid outline, eventually becomes consumed duringoperation and wears down to a pointed shape shown by the chain-dottedline 2. The end is socketed at 3 to receive a truncated tapered spigot 4of a replacement electrode 5, in a sleeve joint. The thickness of thewall between the exterior surface of the used electrode at 2 and theinternal surface of the female recess 3 steadily decreases during theconsumption of the electrode.

If the diameter d of the minimum cross-section of the tapered spigot 4of the male end of electrode 5 is too great in relation to the diameterof the concentric crosssection of the end 2 of a carbon 1, i.e., theWall thickness as referred to above, there is a risk that the end 2shown by chain-dotted lines will break off and since the arc strikes atthis part the arc would become extinguished.

As the new electrode commences to burn away, its contours formcontinuations of the part 2, as indicated by the dotted line 5a.

FIGURE 2 shows in axial section known negative carbon electrodes similarto those of FIGURE 1. Here again the nearly consumed electrode 6 and anew carbon 7 are connected by a sleeve joint in the form of a taperedspigot 8 fitting into a socket 9 in the end of electrode 6. The diameterof the minimum cross-section d2 of the spigot 8 is less than thediameter d1 of spigot 4 of FIG- URE 1. The remaining part 10 of theelectrode 6 is defined by the chain-dotted line. The breaking off ofpart 10 cannot be avoided, but the part 10 is shorter than the part 2 ofFIGURE 1, and the arc re-strikes immediately on the new electrodewithout becoming extinguished. In fact the temperature of the remainingpart 10 of the used-up electrode or of the male spigot 8 is sufficientlyhigh that the ionisation level at this place aids the restriking of thearc. However the arc is disturbed by the placement of the cathodic areaon the plane surface of the cross-section of the tapered portion. Thedotted line 7a indicates the burn-off portion of the new electrode. Thespigot 8 is joined to the socket 9 by a disc of a thermo-setting resinsuch as Bakelite which melts during operation and runs, which is anuisance so far as good operation is concerned.

FIGURE 3 shows in axial section two negative carbon electrodes somewhatsimilar to the negative electrodes shown in FIGURES 1 and 2, butconnected by a sleevejoint according to the invention which is acombination of -a tapered point and truncated taper. The female orsocketed end 11 of the used-up electrode 12 is joined to the male end ofthe new electrode 13 by means of a sleeve joint comprising a taper 14extended to a small tapered point 15, the end of which, because of itsadvance location in the part 16 (indicated by chain-dotted lines) of theused-up carbon, is brought to a temperature near that of the cathodicarea before the part 16 is broken. At that moment the arc is immediatelyre-struck without difliculty, to the end of the small tapered point 15,the shape of which favours the fixation of the cathodic area and theionisation level of which is very slightly different from the normalionisation level of the cathodic area. The burn-ofi portion of the newelectrode is indicated at 13a.

FIGURE 4 shows one end of each of the two electrodes according to theinvention and of the kind shown in FIGURE 3, but in the separatedcondition. On the left is the female or socketed end, shown in section,the truncated tapered part 11 being extended by a tapered recess 17 andon the right the male or spigoted end.

FIGURES 5 and 6 show schematically a carbon arc lamp utilisingcontinuous combustion negative carbon electrodes according to theinvention with the anode 20 and its current lead-in and holder. Thelight emission is mainly from the spot at the anode. According to'thedirection in which it is desired to project the light the anode may bearranged at various angles in a vertical plane. The angle of the cathodemay be suitably adapted is known manner.

FIGURE 5 shows the negative electrode 12 in the course of combustion,partially sectioned at its base in order to show the female fitting 11.The new electrode 13 is shown fitted in the electrode 12 in the courseof combustion. The operation of fitting one electrode into the other maybe carried out manually or mechanically. The conical part 11 is arrangedto provide adherence for the forward electrode 12 to carry with it theelectrode 13 in its arc-ward movement.

FIGURE 6 shows the negative electrode 12 when nearly consumed, the newelectrode 13 having already been taken by the feed rollers 18. Thequantity of carbonaceous material of the electrode 12 remaining aroundthe female fitting 11 is sufiicient to allow the passage of the electriccurrent. The distance between the cathodic spot 25 and the apex of theconical part 15 of the fitting is relatively small, this small distancepermitting the transmission of the heat from the cathodic spot to theapex of the cone 15 so that the arc is regenerated without interruptionon this same apex of the cone 15. The cathodic spot is thus maintainedalong the axis of the negative electrode.

It will be understood that the male or spigoted end is inserted into thefemale or socketed end of an electrode already in operation before thelatter is used up or completely consumed. It will also be appreciatedthat an electrode according to the invention preferably has one endformed with a male spigot and its other end with a female socket.Essentially, however, the electrode only has the rear end formed with afemale socket-the other end may be the same as a conventional electrode.This is of use for initially striking an are where a shaped end is notnecessary and may even be undesirable.

The tapered sleeve joints operate to best advantage if the degree oftaper of the female and male parts is the same. The preferred taperangle is from 4 to 7.

The ratio between the diameter of the cross-section at the widest partof the taper to the exterior diameter of the generally cylindricalnegative carbon may vary between 0.45 and 0.55. The ratio between thelength of the taper to the exterior diameter of the cross-section of thenegative carbon may vary between 0.75 and 0.91.

The taper angle of the tapered point 15 of the male spigot 15 of FIGURES3 and 4 is at least and the tapered end recess 17 of the female socket11 is also 90".

The provision of the tapered point 15 has the advantage of ensuring therapid passage of the are from the end in the course of combustion tothat of the new carbon without exaggerated heatin at the junction.

The taper angle of the two tapering parts of the joint should not exceed7, because the axial cleavage stress between the male and femaleextremities must be greater than that produced by the expansion of theair and of the gases trapped in the bottom of the cavity of the femalepart, otherwise there may be premature projections of the piece of thefemale sleeve and extinguishing of the are.

It is clear that the invention applies to negative carbons of alllengths operating with direct current whatever their rate of wear.

The external oxidation of the negative electrode produces a taperedshape 16, the cross-sectional area of which decreases from the currentlead-in part 19 up to the location of the cathodic spot 25. Thedimensions of the male and female conical parts are arranged to be suchthat the above-mentioned tapering does not lead to a premature fractureof the female rearward part of the electrode in the course ofcombustion. This premature fracture would involve undesirable extinctionof the arc.

Moreover, it is important to ensure the maintenance of the cathodic spot25 along the axis of the negative electrode when the arc has to passfrom the electrode in the course of combustion to the followingelectrode; to this end, the truncated part of the joint is prolonged bythe conical part 15.

The male and female sleeve junctions may be formed by any appropriatemachine-tool means, e.g. a lathe, particularly a screw-cutting latheafter having square-cut the graphitic or graphitised cylindrical rods.Suitable dimensions for a negative electrode with a diameter of 11 mm.are given below:

Length of truncated conical portion 14 mm Length of pointed portion 15mm 2.1 Diameter of base of truncated conical portion 14 mm 5 Diameter ofbase of pointed portion 15 mm 4.26 Apex angle of pointed portion 15degrees 90 Angle of conical portion 14 do 4 These negative electrodesoperated effectively at the following parameters:

240 amp., 56 volts (13.44 kw.) 350 amp, 70 volts (24.5 kw.) 400 amp, 80volts (32 kw.)

For these conditions, the length of negative electrode emerging from thecurrent lead-in 19, in other words the protrusion, was between 25 mm.and 35 mm.

At the moment when the arc passes, in the course of combustion, from theremnant 12 to the new electrode 13, a small fragment of the electrode 12is observed to drop off, this fragment comprising a portion between thecathodic spot 25 and the tip of the cone 15. The tip of the cone 15 ofthe male fitting being thus heated sulficiently to raise its temperatureto a high value, the arc is immediately restarted on said tip 15.

It should be understood that the foregoing description of specificembodiments is for the purpose of illustration only and that variousmodifications may be made without departing from the scope of theinvention as defined in the appended claims.

I claim:

1. A negative electrode for a high intensity carbon arc lamp, saidelectrode having a male end formed to fit into a complementarily-sha'pedfemale end of another electrode and being adapted to burn from said maleend towards said female end, said male end being in the form of atruncated conical portion terminating in a pointed portion, the angle oftaper of said pointed portion being greater than that of said truncatedconical portion, said electrode having a female socket at one end in theform of a truncated conical bore extended by a tapered recess, the angleof taper of said truncated conical bore and of said truncated conicalportion lying between 4 and 7.

2. A negative electrode for a high intensity carbon arc lamp as setforth in claim 1, wherein the ratio between the largest width of saidtruncated conical portion and the exterior width of the electrode in thesame radial plane lies between 0.45 and 0.55.

3. A negative electrode for a high intensity carbon arc lamp, saidelectrode having a male end formed to fit into a complementarily-shapedfemale end of another electrode and being adapted to burn from saidrnale end towards said female end, said male end being in the form of atruncated conical portion terminating in a pointed portion, the angle oftaper of said pointed portion being greater than that of said truncatedconical portion, the ratio of the length of said truncated conicalportion and said pointed portion to the diameter of the electrode lyingbetween 0.75 and 0.91.

4. A negative electrode for a high intensity carbon arc lamp, saidelectrode having a male end formed to fit into a complementarily-shapedfemale end of another electrode and being adapted to burn from said maleend towards said female end, said male end being in the form of atruncated conical portion terminating in a pointed portion, the angle oftaper of said pointed portion being greater than that of said truncatedconical portion, the angle of said pointed portion being at least 5. Anegative elect-rode for a high intensity carbon arc lamp, said electrodehaving a male end formed to fit into a complementarity-shaped female endof another electrode and being adapted to burn from said male endtowards said female end, said male end being in the form of a truncatedconical portion terminating in a pointed portion, the angle of taper ofsaid pointed portion being greater than that of said truncated conicalportion, said electrode having a female socket at one end in the form ofa truncated conical lbore, extended by a tapered recess, having an angleof taper of 90.

References Cited UNITED STATES PATENTS 863,674 8/1907 Tone 3133571,253,572 1/1918 Buchanan 313357 2,024,445 12/ 1935 Gatehouse 3 l33572,693,498 11/1954 Penberthy 313-357 3,030,544 4/1962 Gambooldi et a1.313357 3,131,290 4/1964 Stepath 313355 FOREIGN PATENTS 1,383,904 11/1964France.

3,315 1878 Great Britain. 8,781 6/1884 Great Britain.

JOHN W. HUCKERT, Primary Examiner.

A. J. JAMES, Assistant Examiner.

